Pivotal role of the sub-supracardinal anastomosis in the development and course of the left renal vein.

A retroaortic left renal vein is encountered frequently in the dissecting room and in radiological investigations. A number of recent reports of this variation led us to review the development of the renal veins and the inferior vena cava to understand its etiology. For further insight, we also examined our collection of serial sections of cat embryos. In human embryos of about 15 mm the "renal collar," a venous ring around the aorta, is formed by anastomoses between subcardinal and supracardinal veins. The ventral part of the "renal collar" is formed from the intersubcardinal anastomosis, the dorsal part from the intersupracardinal anastomosis and the lateral parts from the sub-supracardinal anastomoses. The primitive renal veins drain venous blood from the metanephros into the sub-supracardinal anastomoses. A retroaortic left renal vein would form if the dorsal part of the sub-supracardinal anastomosis and the intersupracardinal anastomosis persist whereas the ventral part of the sub-supracardinal anastomosis and the intersubcardinal anastomosis regress.